Amino acids deeply relate to tastes of foods such as body, sweetness, etc. thereof, and, in addition, a biological activity of amino acids has attracted attention in recent years, especially. Accordingly, various products characterized by amino acid contents have been developed. Further, agricultural products are strongly interested in nutritional values thereof.
It is known that an amino acid content in a plant changes depending on a cultivation condition of the plant. For example, Non-patent Literature 1 discloses that a content and a composition of a free amino acid in cabbage change depending on a harvesting stage and a nitrogen fertilizing condition. Non-patent Literature 2 discloses that a free amino acid content in spinach differs depending on differences in soil and fertilizer.
It is also known a technique for producing vegetables having high amino acid contents. For example, Patent Literature 1 discloses a method of producing a vegetable having a high amino acid content, in which method a nitrogen fertilizer is supplied to the vegetable at a harvesting stage thereof. Patent Literatures 2 through 4 each disclose that a free amino acid content is increased in a plant transformed with a certain gene.